Bicarbonate is one variable of the main chemical composition in the water column if the world’s rivers, affected by many factors such as lithological – geological characteristics, weathering processes, meteorological and hydrological characteristics, relative altitudes of the watershed and human activities. This paper presented the observation results of bicarbonate concentration in the Red River, from the upstream to the downstream area, including urban rivers in Hanoi during the monthly sampling period from January to December 2019. The results showed that HCO3− concentrations at 12 observed sites of the Red River system arranged from 87.3 to 423.9 mg/L, averaging 149.5± 89.4 mg/L for all sites. The significant difference in HCO3− concentrations between the Red River upstream sites and the urban river sites reflected an important impact of human activities on riverine bicarbonate concentrations. Besides, HCO3− concentrations in the Red River water also depended strongly on meteorological and hydrological characteristics, land use and agricultural practices as well as lithological and geological characteristics. Long term observation should be carried out for determining the change of bicarbonate concentrations and fluxes of the Red River toward the South Asian Sea.